This invention relates to a noise eliminating filter for eliminating unwanted signals from electronic equipment by grounding such signals.
Generally, in order to prevent noise generation caused by unwanted signals in electronic equipment, a noise eliminating filter (electromagnetic interference filter) as shown in an equivalent circuit diagram in FIG. 1 is incorporated in the circuit to thereby ground unwanted signals.
The conventional noise eliminating filter used for the above purpose, as shown in FIG. 2, has been so constructed that a mounting male screw thread 12 is formed on the outer periphery of the lower half of a tubular metal casing 11 and a projection 13 is provided inside the lower end of casing 11 to thereby support a lower-stage capacitor 14 and a magnetic material 15 (e.g. ferrite beads); a larger diameter support 17 for supporting an upper-stage capacitor 16 is provided within the upper portion of metal casing 11, and a feedthrough terminal 18 passes through the upper and lower stage capacitors 16 and 14 and the magnetic material 15.
However, in the metal casing 11 constructed so as to contain the lower-stage capacitor 14 together with the magnetic material 15, the lower-stage capacitor 14 should be equal in the size to the magnetic material 15. The upper-stage capacitor 16 must also be supported by the metal casing 11, which results in the inconvenience of requiring the preparation of capacitors of two different sizes.
Also, a smaller inner diameter d of the metal casing 11 must be larger than an outside diameter of the lower-stage capacitor 14 so that the male screw thread 12 portion of the metal casing 11 must be fabricated with a smaller thickness which results in a lower mechanical strength thereof, thereby causing a problem in that the noise eliminating filter cannot actually be made small in size and lightweight.